Odds are far better than good that your high performers are achieving what appears to be high levels of productivity by building technical debt into the application by taking shortcuts whether intentionally or unintentionally. Examples of shortcuts are not taking the time to design and architect things well at all levels (low to high — think objects and object hierarchies, database schema changes, etc.), failing to test adequately, and crafting code that is hard to read, maintain and extend.

These kinds of high performers are actually low performers when when TCO is factored in.